This invention relates generally to electrically controlled fuel injectors and, more particularly, to fuel injectors with a directly controlled dual concentric check valve.
In a dual fuel engine, a fuel injector is used to inject liquid fuel, such as diesel distillate, into the engine cylinder, and a second system is responsible for delivering a second type of fuel, such as natural gas. For such dual fuel engines it is desirable to be able to inject two distinct quantities of liquid fuel. A small pilot injection of diesel fuel is used to assist in ignition of a main charge of gaseous fuel when the engine is operating in dual fuel mode. However, when gaseous fuel is unavailable, or for some other reason diesel-only operation of the engine is desired, a larger injection of only diesel is made.
In the past, it would have been necessary to use two separate fuel injectors, or at least two separate nozzle assemblies in an engine with these operating requirements. One nozzle would have been necessary for the small initial pilot injection, and a second nozzle would have been necessary for the larger diesel-only injection. Such systems tend to be complex and difficult to control. It is thus desirable to create a system capable of fulfilling the dual fuel injection requirements with a single injector.
A dual concentric check design is known in the art. Lauren W. Burnett invented one example of such an injector in 1989 that could be used to inject both liquid fuel and slurry fuel through concentric nozzle outlets. It is shown in U.S. Pat. No. 4,856,713. However, this injector is not directly controlled, and designed for a liquid or slurry mixture injection rather than for use in a dual fuel engine.
A typical diesel engine must operate with a broad range of fuel quantities and operating speeds. The necessary precision of injection timing, injection duration, and the provision of sufficient pressure are difficult to accomplish with a single fuel injector. Direct control allows for better performance by enabling the precise control of injection timing and duration. As a result, the engine operates more efficiently and the fuel burns more completely, producing lower emissions.
The present invention is directed to overcoming one or more of the problems and disadvantages set forth above.
A directly controlled dual concentric check fuel injector has an injector body that defines a nozzle chamber, a check control chamber, and a plurality of nozzle outlets. A dual concentric check assembly is at least partially positioned in the injector body, and has a closing hydraulic surface exposed to fluid pressure in the check control chamber. The dual concentric check assembly is movable between a first position in which the nozzle outlets are blocked, a second position in which a first portion of the nozzle outlets are open, and a third position in which a second portion of the nozzle outlets are open.
In another aspect, a method of injecting fuel includes a step of providing a fuel injector with a plurality of nozzle outlets and a directly controlled dual concentric check assembly. The check assembly has a closing hydraulic surface exposed to fluid pressure in a check control chamber. The check control chamber is connected to a low pressure passage. The check assembly is moved to a configuration in which at least a portion of the nozzle outlets are open. Finally, the check control chamber is connected to a high pressure passage.
In still another aspect, the dual fuel engine includes a plurality of directly controlled dual concentric check fuel injectors attached to an engine housing. Each of these injectors has a dual concentric check assembly at least partially positioned in the injector body. Each of the assemblies has a closing hydraulic surface that is exposed to fluid pressure in a check control chamber. The dual concentric check assembly is movable between a first configuration in which the nozzle outlets are blocked, a second configuration in which a first portion of the nozzle outlets are open, and a third configuration in which all of the nozzle outlets are open. A source of liquid fuel is fluidly connected to the fuel injectors.